Angular-velocity stabilizer for rotatable gear-driven shafts



Oct. 9, 1928.

A. J. HOLMAN ANGULAR VELOCITY STABILIZER FOR ROTATABLE GEAR DRIVEN SHAFTS Filed Aug. 18, 1927 Patented Get. 9, 1928.

esiren "STATES ARTHUR J'. HOLMAN, OF BOSTON, MASSACHUSETTS.

ANGULAB-VELOCITY STABILIZER FOR ROTATABLE GEAR-DRIVEN VSHAFTS.

Application filed August 18, 1927. Serial No. 213,793.

Ithas beenthe object of my invention to provide a means for-securing uniform angular velocity of a pair of rotatable shafts such as are employed to support and revolve the overlapping lens discs in a moving picture projector of the type shown in my Letters Patent of the United States No. 1,534,098 dated May 11, 1926. In such a device 1t 1s 1m; portant to maintain the exact registrationof the lens centers of overlapping rotatable disc elements at the moment when corresponding pairs of disc element centers cross the optical axisof the complete lens system; It is also necessaryto maintain the intended angular relation between coacting lens centers in the revolving discs all times. As the rotatable discs are gear driven through worm gears mounted thereon and actuated by worms,

mounted on a common drive shaft, it is apparent that the development of back-lash in the gear trains will have the effect of producing variation in the angular velocity of the shafts on which the rotatable discs are mounted, thus disturbing the intended angu lar relation between coacting lens centers" in the rotatable discs and also disturbing the intended condition of registration of coactmg lens centers on the optical axis To correct the tendency of back-lash in such a device and to secure uniform wear on the gears so that the effect of wear may be compensated automatically, 1 have made the s ccial object of my invention to provide a device of the character indicated which shall influence each rotating shaft in a precisely similar manner and with equal friction torque and which shall provide means for the delicate adjustn'ient of the friction torque required in such a device.

My device may be best understood by reference to the accompanying drawing which shows a front view of a moving picture projector of the type shown in my said patent, having the front cover-plate of the rotatable disc housing and the front ob ective removed, and showing my angular velocity stabilizer in connection with the shafts whereon the re volving discs are mounted.

Referring now more specifically to the drawing, 1 is the front of the main casing of the projector mechanism on wh ch is mounted the rotatable disc housing 2 within which 1s mounted a web 3 secured in position by the screw posts 4. Bearing brackets 5 and 5, supporting the front ends of shafts 6 and 6, are mounted on the web 3. The shafts 6 and 6 have fast mounted thereon rotatable lens discs 7 and7 constructed and arranged in overlapping position, and said shafts are each provided with a worm gear meshing with a driving worm on a common drive shaft as described in my said patent.

c Upon the outer extremities of the shafts (3 and 6 are fast mounted grooved pulleys or brake-wheels 8 and 8. A flexible belt 9. preferably a woven fabric cord,is attached at each end tolposts 10 and 10 fixed in the web 3 and tits in the grooves of the brake-wheels 8 and 8 embracing the greater part of the circumference of each of said wheels, being held in contact therewith by idler rollers 11 and 11 I mounted on said web 3. V

A lever arm 12 mounted on web 3 by the pivot screw 13 carries at one end a roller 14 which bears upon the belt 9 at a point sub stantially midway between the idler rollers 11 and 11 To the other end of the lever 12 is attached the spring 15 to which is connected a chain 16 which passes around a grooved ratchet wheel 17 mounted on web 3 by screwpost 18. The end of the chain 16 is attached to the ratchet wheel 17. A pawl 19 engages the teeth on ratchet wheel 17 and prevents its counter clockwise rotation. The pawl 19is held in engagement with the ratchet wheel 17 by the thrust of a coil spring contained within the cylindrical boss 20 on the web 3. The boss 20 bears a V-shaped indicator 21 prejecting partly across the face of the ratchet wheel 17 on which may be placed suitable graduation marks (not shown) to indicate the posi tion of setting of the ratchet wheel 17. 7

It will be readily understood from the foregoing that the friction of the belt 9 upon the brake-wheels 8 and 8, as brake-wheel 8 is rotated clockwise and brake-wheelS is rotated counter clockwise, will prevent backlash in brake-wheels, the belt being maintained in 7 contact with each brake-wheel over an arc of its circumference which is alike in each in stance. It is particularly desirable to avoid excess friction and load upon the gears in such a device 1n order that as little Wear of moving parts may occur as possib1e,-and my device well meets this requirement as it is v susceptible to very delicate adpistmen't inasmuch as a very slight increase in belt tension at the middle portion is multiplied toward the ends of the belt owing to the direction of rotation of the brake-wheels. This delicate adjustment may be obtained by turning the ratchet wheel 17 so as to vary the tension of the spring by which thelever 12 is influenced so .as to regulate the belt tension at the middle portion.

The desired adjustment of belt tension is largely determined by trial and graduation marks upon the ratchet wheel 17 to be read in connection with the indicator 21 will as sist in resetting the device in case the ad justment is disturbed for any reason.

Having thus fully described my invention, what I claim is,

1.111 a device of the character specified the combination of a pair of gear driven rotatable shafts arranged to rotate in opposite directions, brake-wheels fast mounted on said shafts, a belt arranged to contact with equal arcs on said brake-wheels, and means for varying the tension-0t said belt.

2. In a device of the character specified the combination of a pair of gear driven ro tatable shafts arranged to rotate inopposit dlrections, brake-Wheels fast mounted on said shafts, a belt secured ateach end and ar+ ranged to contact with equal arcs on said brake-wheels, a pressure member arranged to contactwith that portion ofthe bQlUWlllCh is substantially 'midway between its points of contact with said brake-wheels and means tor varyin the influence of said pressure men'iber so as variously to deflect said'belt thereby and vary the tension thereof.

shafts, a belt secured at each end and arranged to contact with equal arcs on said brake-wheels, a pivotallyn'iounted lever arm, a roller mounted on one end of said lever arm and arrangedto bear upon said belt at a point substantially midway between its points of contact with said brakewheels, a coil spring attached to the other end of said lever arm, a flexible member attached to said coil spring, a ratchet-wheel to which said flexible member is attached and uponwhich said flexible member may be wound in order to v ry the tension of said spring, and a pawl arranged to retain'said ratchetheelagainst unwinding rotation.

ARTHUR J. HOLMAN. 

